The impact of terrestrial and estuarial factors on the density of environmental bacterial (Vibrionaceae) and faecal coliforms in coastal water.

A study of the densities of faecal coliforms, Vibrio anguillarum, Vibrio alginolyticus and Aeromonas hydrophila in Danish bathing areas was carried out over the period May-October, 1981 with special reference to specific terrestrial and estuarial determinants. Significant correlations were found between V. anguillarum and V. alginolyticus (r = 0.57) and A. hydrophila and faecal coliforms (r = 0.43). The densities of the Vibrios were highly influenced by temperature and distance from pollution source, while salinity was of minor importance. R2 values for V. anguillarum, V. alginolyticus and A. hydrophila of 0.54, 0.51 and 0.40, respectively, indicate that these organisms were superior to faecal coliforms (R2 = 0.21) in characterizing the local conditions. The following levels were used as relevant to characterize an environmental risk: faecal coliforms 1000/100 ml, V. anguillarum 10000/100 ml, V. alginolyticus 500/100 ml and A. hydrophila 500/100 ml. It was found that the position of sampling site, discharge with the current, and uncontrolled outlets influence the frequency of violations. At certain sites coincidence of violations for both faecal and environmental bacteria indicated a simultaneous existence of a faecal and "organic" pollution. At other sampling sites high levels of environmental bacteria only should be considered important to the evaluation of the hygienic quality of the water.